Coal-burning power plants around the country spew toxic gases known to cause everything from birth defects, cancer and heart attacks to asthma and bronchitis. They poison lakes and streams, and the fish we eat, with mercury.

Unfortunately, we still rely on them to provide about 45 percent of our electricity. So earlier this month, federal officials proposed the first national standard to regulate emissions of mercury and other pollutants from dirty power plants. Besides protecting the public, the new rules — to be implemented in three or four years — will encourage more of these old coal-fired plants to convert to natural gas, the cleanest of the fossil fuels, or to shut down entirely.

New Jersey already has similarly strict standards for its own coal-fired plants, which it had to impose under the Clean Air Act in 2009 because it had so much pollution already. But the proposed national rules still come as a relief, because our state continues to be choked by toxic air that wafts in from plants in Pennsylvania, Ohio and Midwestern states, accounting for about one third of our air pollution. Federal officials would compel changes to dirty plants that still have no smokestack scrubbers, the filters now standard on modern coal plants, which can capture 95 percent of key pollutants.

Installing and maintaining such pollution controls on all of the nation’s coal plants is estimated to cost a total of about $10 billion. Utility companies and their Republican supporters argue that’s too expensive. They are likely to mount a strong challenge to Lisa Jackson, chief of the Environmental Protection Agency, who has been fending off Republican attempts to impose new limits on her power to regulate carbon under the 1970 Clean Air Act. It will be a tough fight, but worth it: this new policy would prevent thousands of deaths and tens of thousands of illnesses a year, according to the EPA. And it would result in health and environmental benefits of more than $100 billion a year.

When industry lobbyists complain about cost, environmentalists point out that coal is expensive, too. Its prices have increased due to higher production costs linked to tougher regulations and more demand from China.

Meanwhile, natural gas prices are low and are expected to remain that way. If utility companies don’t want to waste money by upgrading older coal plants to meet the new rules, they shouldn’t: Convert them to natural gas, instead.